Ink-jet recording head and ink-jet recorder

ABSTRACT

The recording electrodes and the control electrodes of an ink jet recording head are alternately arranged on a substrate. Ink in which coloring material is distributed in a solvent is supplied to the recording electrode so that the ink can flow in the direction of the length of the recording electrode. An ink circulation part is provided for collecting surplus ink from the point of the recording electrode from which ink is discharged. As a result, an ink jet recorder, which can produce a high definition image without shifting the ink impact position on the recording medium, can be produced.

TECHNICAL FIELD

The present invention relates to an ink jet recording head and an inkjet recorder of the type used to print an image by discharging ink dropsfrom an electrode of the recording head and propelling them onto arecording medium.

BACKGROUND OF THE INVENTION

An ink jet recorder discharges ink droplets from a discharge opening andguides them onto a recording medium. The dots are formed by leading inkfrom an ink tank to each discharge opening and applying kinetic energyto the ink, so that a small amount of ink in the form of a drop isdischarged from a minute discharge opening, the ink drop is projectedonto a recording medium, and an image is printed.

There is a method (electrostatic recording) of discharging ink by use ofan electrostatic force, in which a voltage is applied between a commonelectrode, which is placed in contact with the recording medium, and arecording electrode, and this is one of the driving methods by whichkinetic energy is applied to the ink. This method is recognized as a wayto achieve high definition in an ink jet printer, because the amount ofink discharged on recording medium can be controlled bypulse-width-modulating the voltage applied to the recording electrode.

An example of such a method is disclosed in the Patent ApplicationLaid-open No.7-502218 (PCT), in which ink, in which a coloring materialis dissolved in a solvent in a low concentration, is supplied to thesurface of the recording electrode, an electric field is formed byapplying a voltage to the recording electrode, the coloring materialsubjected to the electric charge is agglutinated, and the agglutinatedcoloring material is discharged from the recording electrode on a pathtoward the recording medium. Further, the technology concerning thestructure of the recording head in a recording method similar to theabove-mentioned example is described in the Japanese Patent ApplicationLaid-Open No. 11-34338.

SUMMARY OF THE INVENTION

An image is recorded by discharging agglutinated coloring material ontoa recording medium by applying an electrical bias to the recordingelectrode, while making the ink circulate, collecting the ink in whichthe coloring material is agglutinated on the point of the recordingelectrode, and superimposing a pulse voltage on the electrical bias ofthe recording electrode in this state, thereby effecting electrostaticrecording as disclosed in the above-mentioned official report.

Further, clogging of the ink is not generated easily in general inelectrostatic recording because a small hole does not exist in the inkdischarge part. Therefore, even if the recording head is manufactured inthe form of a line head, a defective portion where discharge is notperformed is not generated easily. Therefore, an ink jet recorder whichhas a line head can be achieved. There is a feature that it is possibleto print at high speed because the record recorder with a line head canrecord on the recording medium at the same time in the omnidirection ofwidth. However, because it is necessary to discharge the coloringmaterial agglutinated at the point of the recording electrode in themethod disclosed in the above-mentioned official report, it is necessaryto supply a large amount of coloring material to print at high speedusing high-speed ink circulation. Further, there is a limitation inmaking ink circulate at high speed in the flight channel (Hereaftersimply called the channel) formed by micro-fabrication. Further, it isnecessary to manufacture a lot of channels without a defect to achieve aline head. Further, it is necessary to have the same printcharacteristic in the press by all channels. Therefore, it becomesimportant to arrange the shape of a lot of the channels when a line headis manufactured, and to manufacture it cheaply and easily.

Further, when the interval of the recording electrode narrows, thedischarge is influenced easily by the electric field generated by thevoltage applied to the adjacent recording electrode in this recordingmethod. There is also the displacement of the impact position of thedischarge as a problem which occurs due to the influence of thiselectric field. The cause of this problem will be explained as follows.

The voltage applied to recording electrodes A and B, when a discharge isto be produced from the recording electrodes A and B and is not to beproduced from an electrode C among three recording electrodes A, B, andC, increases more than the voltage applied to recording electrode C.Therefore, the component of the electric field directed to the recordingelectrode C is generated in the electric field in the vicinity of thepoint of recording electrode B. Therefore, the discharge produced fromrecording electrode B is impacted so as to approach the position on therecording medium where recoding is to be effected by recording electrodeC. As a result, a problem of distortion of the image on the recordingmedium and a deterioration of the picture quality occurs. To prevent thepotential applied to a recording electrode from being transferred to anadjacent recording electrode through the ink, the ink is divided intoparts in each channel by providing a member for partitioning ink betweenrecording electrodes arranged in a line. Therefore, not enough effect isachieved, though the displacement of the impact position of thedischarge is reduced. Because the configuration disclosed in PatentApplication Laid-Open No. 7-502218 (PCT) does not have a partitionbetween recording electrodes arranged in a line, the displacement of theimpact position of the discharge increases easily, when printing.

Further, each channel is divided by a partition, and the recordingelectrode is arranged at the position which comes in contact with inkwhich flows in the channel in the configuration disclosed theabove-mentioned Japanese Patent Application Laid-Open No. 11-34338.Therefore, not enough effect is achieved, though the displacement of theimpact position of the discharge is reduced.

Further, the recording head described in the above-mentioned officialreport has a relief structure formed from the ink channel bottom and thewall which partitions each ink channel. Therefore, costs of manufactureare high because the relief structure needs to be manufactured by usingeither a method of bonding with accumulating a concave part and a convexpart or a method of cutting down the concave part using a dicer, etc.

Further, the recording head described in the above-mentioned officialreport does not have means to optimize the curve profile of the liquidlevel of ink (hereafter called an ink meniscus) due to the surfacetension of the ink generated on the point of said recording electrode,which influences the concentration of the electric field on the point ofthe recording electrode of each channel. Because the concentration ofthe electric field on the point of the recording electrode is weak, itis necessary to raise the voltage applied to the recording electrode foreffecting a discharge. As a result, the driving circuit for applying thevoltage becomes expensive and the amount of flight of the discharge doesnot becomes uniform.

The present invention is directed toward solving the above-mentionedproblems.

An object of the present invention is to provide an ink jet recordinghead which can prevent the impact position of the discharge fromshifting and obtain a high definition image.

Another object of the present invention is to provide an ink jetrecording head in which the shape of a lot of channels can be easilymade uniform when line heads are manufactured, and which can bemanufactured cheaply and easily.

Another object of the present invention is to provide an ink jetrecording head which can be driven at a low voltage and in which theamount of discharge of ink can be made uniform.

Another object of the present invention is to provide an ink jetrecording head which can print at high speed.

In accordance with the present invention, an ink jet recording head hasa substrate, a plurality of recording electrodes arranged on saidsubstrate, a plurality of control electrodes arranged so as to sandwicheach of said recording electrodes, and an ink circulation part forsupplying ink, which contains coloring material in a solvent, to saidrecording electrodes, to cause it to flow in a direction of the lengthof said recording electrode, and for collecting said ink from the pointof said recording electrode.

The electric potential applied to the recording electrode of the channelfrom which ink is discharged is prevented from being shifted to asurrounding channel by individually providing ink channel for everychannel through which ink passes. As a result, the electric fielddistribution around the recording electrode in the channel from whichink is discharged is stabilized, and the direction of ink discharge isstabilized. Further, the electric field distribution at the point of therecording electrode from which ink is discharged is stabilized and thedirection of the ink discharge is stabilized by setting up controlelectrodes so as to sandwich the recording electrode and by applyingconstant potential to the control electrodes.

Further, an electrical discharge due to the electric breakdown of air isprevented by applying a protection film on the recording electrode.

Further, the ambient air along with ink from the recording electrode toink collection channel is collected. The ink meniscus form is controlledby the collected air flow, and a low voltage drive and a uniform inkflight amount are made possible.

Further, the ratio of the insoluble material, such as the coloringmaterial contained in the discharged ink is made lower than the ratio ofthe solvent, and printing speed is increased.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are sectional views of an ink discharge portion ofan ink jet recording head according to the present invention, takenalong lines a-a′ and b-b′, respectively, in FIG. 2.

FIG. 2 is a sectional view taken along the line c-c′ in FIG. 1.

FIG. 3 is a sectional view taken along the line d-d′ in FIG. 1.

FIG. 4 is a sectional view of an ink jet recorder according to thepresent invention.

FIG. 5 is a schematic diagram showing the configuration of an ink jetrecording head according to the present invention.

FIG. 6 is a diagram illustrating the method of adjusting ink pressure inthe ink circulation system shown in FIG. 5.

FIG. 7 is a sectional view showing the configuration, besides the inkdischarge portion of FIG. 1, of the ink jet recording head according tothe present invention.

FIGS. 8(a) to 8(e) are section views which illustrate successive stepsin one example of the method of manufacturing the ink discharge portionaccording to the present invention, and FIGS. 8(a)(1) to 8(e)(1) are topplan views of the structures illustrated in FIGS. 8(a) to 8(e),respectively.

FIGS. 9(a) to 9(d) are section views which illustrate further successivesteps of the method of manufacturing the ink discharge portion accordingto the present invention, and FIGS. 9(a)(1) to 9(d)(1) are top planviews of the structures illustrated in FIGS. 9(a) to 9(d), respectively.

FIGS. 10(a) to 10(e) are section views which illustrate furthersuccessive steps of the method of manufacturing the ink dischargeportion according to the present invention, and FIGS. 10(a)(1) to10(e)(1) are top plan views of the structures illustrated in FIGS. 10(a)to 10(e), respectively.

FIG. 11 is a sectional view of the configuration of the ink dischargeportion of the present invention.

FIG. 12 is a sectional view showing an ink meniscus formed near therecording electrode in the ink discharge portion.

FIG. 13 is a diagram showing the ink meniscus formed near the recordingelectrode in the ink discharge portion.

FIG. 14 is a cross-sectional view showing another embodiment of the inkdischarge portion of the ink jet recording head according to the presentinvention.

FIG. 15 is a sectional view taken along the line a-a′ in FIG. 14.

FIG. 16 is a sectional view taken along the line b-b′ in FIG. 15.

FIG. 17 is a diagram showing the ink meniscus formed near the recordingelectrode in the ink discharge portion of FIG. 15.

FIG. 18 is a diagram showing the ink meniscus formed near the recordingelectrode in the ink discharge portion of FIG. 14.

FIG. 19 is a schematic diagram showing another embodiment of the ink jetrecording head according to the present invention.

FIG. 20 is a diagram showing an enlarged view of a part of FIG. 19.

FIG. 21 is a sectional view of another embodiment of the ink dischargeportion in the ink jet recording head according to the presentinvention.

FIG. 22 is a sectional view taken along the line c-c′ in FIG. 21.

FIG. 23 is a left side view of ink discharge portion in FIG. 21.

FIG. 24 is a schematic diagram of another embodiment of the inkdischarge portion in the ink jet recording head according to the presentinvention.

FIG. 25 is a sectional view of another embodiment of the ink dischargeportion in ink jet recording head according to the present invention.

FIG. 26 is a schematic diagram showing another embodiment of the ink jetrecording head according to the present invention.

BEST MODE FOR IMPLEMENTING THE INVENTION

FIG. 4 shows one embodiment of an ink jet recorder according to thepresent invention. The ink jet recorder has a housing 1, a recordinghead 2, an ink tank 3 for replenishment, an ink circulation part 4, inkpart 5, a common electrode 6, a recording medium 7 and a recordingmedium carrying passage 8. A grounded common electrode 6, a recordinghead 2 arranged so that the ink discharge entrance is directed to saidcommon electrode 6, a recording medium carrier device for passingrecording medium 7 between common electrode 6 and recording head 2, asettling device for settling ink printed on the recording medium, and acontroller for controlling the entire recorder device are provided inthe housing 1 of the ink jet recorder. Ink discharge part 5, a pulsevoltage generation circuit for applying a pulse voltage for inkdischarge to the ink discharge part, and an ink jet recording head whichcontains ink circulation part 4 are integrated with each other.

Details of each part are as follows. Ink discharge part 5 arranged in arow in a direction extending across the recording medium carryingpassage, ink tank 3 for storing ink, ink circulation part 4 forsupplying ink to the ink discharge part 5, a power supply for generatinga record pulse-width modulated voltage according to a picture signalfrom the controller, and a bias supply (not shown) are accommodated inthe recording head 2.

Recording head 2 for each of the cyan, magenta, yellow, and black colorsis at least arranged in the ink jet recorder which is able to print incolor, although the recording head for one color has been shown in FIG.4.

The recording medium carrier device comprises recording medium carryingpassage 8, which is provided from recording medium insertion entrance 1a to recording medium outlet 1 b through the recording position, a pickroller (not shown) which guides the recording medium 7 from therecording medium insertion entrance 1 a to the recording medium carryingpassage 8, a plurality of rollers 9 which come in contact with bothsides of the surface of the recording medium in the carrying passagewith a fixed pressure, and a motor (not shown) etc. which rotates eachroller according to instruction from the controller which controls theentire device.

For instance, ink formed by using a solvent of the petroleum oil group,such as isoparafin of about 10 mPa·s with a low viscosity, or a solventof silicon group, distributing the coloring material, for instance,pigments in said solvent with a dispersing agent and an electrificationcontrol agent, etc., and making the electrified coloring materialparticle can be stored in ink tank 3. Preferably, the electricalresistivity of said ink is 10⁷ Ω·cm or more, the surface tension is 30mN/m or less, and the particle diameter of the coloring material isbetween 50 nm and 500 nm. Further, the surface charge density of thecoloring material particle is preferably between 1 μC/m² and 100 μC/m²,and the content of the coloring material particle is between 1 percentby weight and 10 percent by weight.

The method of circulating ink and the configuration of the ink dischargeportion 5 will be described later in more detail.

First of all, ink circulation part 4 will be explained.

FIG. 5 shows an ink jet recording head, including the configuration ofthe ink circulation portion 4. Ink circulation portion 4 comprises inkholder 21 for holding ink to be circulated, ink flow modulatingcompartment 24 for adjusting ink flow supplied to the ink dischargeportion 5, piping 23 a, 23 b, 23 c, 23 d, 23 e for connecting each ofthese parts, and pumps 22 a, 22 b driven according to control providedby the controller.

Ink circulation portion 4 configured in this way is divided into twosystems, that is, an ink distribution system to supply ink to inkdischarge portion 5, and an ink collection system to collect ink fromthe ink discharge portion 5.

In the ink distribution system, ink stored in the ink holder 21 issucked up with a pump 22 a and is sent to ink flow modulatingcompartment 24. Ink stored in the ink flow modulating compartment 24flows naturally toward ink discharge portion 5, where the dischargeelectrode lines up, because of the pressure due to the potential energydetermined by the liquid level difference between the liquid level ofink in the compartment 24 and that of the ink discharge portion 5. Toprevent the liquid level of ink from changing in the ink modulating flowcompartment 24, an ink liquid level detector 32 for detecting the liquidlevel of the ink is provided in ink flow modulating compartment 24, asshown in FIG. 6. This detection value is fed back to the controller.Therefore, pump 22 a is driven so that the deviation between thedetected value provided by the ink liquid level detector 32 and a setvalue becomes small, so that the amount of ink in the ink flowmodulating compartment 24 is kept almost constant.

On the other hand, ink which has passed through ink discharge part 5 issucked up by the with pump 22 b and collected in the ink holder 21 ofthe ink collection system. Printing by this ink jet recorder is executedafter these ink circulations become stable.

The ink circulation portion 4 shown here is one example, and anotherconfiguration in which ink of a proper amount can be supplied to andcollected from ink discharge part can be adopted.

The configuration of ink discharge portion 5 will be described next.

FIGS. 1(a), 1(b) and FIG. 2 show the configuration of the periphery ofink discharge portion 5 used in the ink jet recorder of the presentinvention. Next, the state in the section (a-a′ section) of recordingelectrode 11 and the section (b-b′ section) of control electrode 12 inthe ink discharge portion 5 shown in FIG. 2 are shown in FIG. 1.

FIG. 1(a) shows a section of the recording electrode 11 as seen alongline a-a′ in FIG. 2. Recording electrode 11, which has a convex part atits point, and control electrodes 12, which are arranged so as tosandwich the recording electrodes 11, are arranged on a substrate 10made of an insulator, such as a glass, with a low permittivity, and therecording electrodes 11 are disposed at a fixed interval in a directionwhich extends across the recording medium carrying passage 8 and arearranged with the points thereof directed toward the common electrode 6.

The width of recording electrode 11 is about 80-150 μm, and the point ofrecording electrode 11 projects from the edge of substrate 10 towardcommon electrode 6 by about 100-200 μm. When the width of the recordingelectrode 11 is too narrow, the channel resistance increases and the inkdoes not flow easily. On the contrary, when the width of recordingelectrode 11 is too narrow, the amount of ink that flows increases andthe ink does not collect easily. As a result, ink may leak into therecorder. Further, when the magnitude of the projection of the recordingelectrode 11 is too small, the amount of ink carried to the point of therecording electrode 11 increases too much, and the amount of the inkflight from the recording electrode 11 is not steady. On the other hand,the amount of ink carried to the point of the recording electrode 11decreases and the ink does not fly when the amount of the projection ofthe recording electrode 11 is too large.

A constant voltage is always applied to control electrode 12 (its widthis about 20-50 μm). As a result, the electric field distribution at thepoint of recording electrode 11 is proper at the time of ink discharge,and the impact position of ink is prevented from shifting. The point ofthe control electrode should project slightly beyond the edge of thesubstrate 10. The electric field at the point of control electrode 12 iseased when the point of control electrode 12 does not project from thesubstrate 10, and thus the installation effect becomes small.

Next, the method of applying a voltage to recording electrode 11 andcontrol electrode 12 will be explained. An electrode bias of about 1.5-2kV is usually applied to each recording electrode 11 in the inkdischarge portion 5 of the recording head 2 by bias supply 15. Inaddition, a pulse voltage of about 0.5 kV is superimposed on theelectrode bias by pulse voltage generation circuit 14 according to therecord signal, and the resultant voltage is applied to this recordingelectrode. Coloring material electrified positively in the ink whichcirculates in the ink circulation system is collected at the point ofthe recording electrode 11 due to application of the electrode bias tothe recording electrode 11. When the pulse voltage is applied, an inkdrop is discharged from the point of the recording electrode 11. The inkdrop is discharged from the point of the recording electrode by theelectrostatic attraction force generated by the electric field formedbetween point 11-1 of the recording electrode and common electrode 6acting on the ink on point 11-1 of said recording electrode, whichelectrostatic attraction force is sufficient to overcome the surfacetension of the ink. Therefore, the discharged ink drop is configured ofan insoluble material which contains an ink solvent and a coloringmaterial. The weight ratio of the coloring material included in the inkdrop increases more than that of the ink which circulates around otherink circulation parts because the above-mentioned coloring material iscollected on the point of the recording electrode. The amount ofinsoluble material containing the coloring material component in theink, which decreases due to said ink drops being discharged on therecording medium, is replenished from ink tank 3. The concentration ofthe insoluble material in the ink stored in ink tank 3 is higher thanthat in the ink which flows in the ink circulation part. This ink isproperly replenished based on the result of detection of theconcentration in the ink circulation part or the result of counting thenumber of print dots.

The voltage in the vicinity of the electrode bias is always applied tocontrol electrode 12. As a result, the electric field distribution atthe point of the recording electrode 11 is stabilized, and the impactposition of ink on the recording medium is prevented from shifting whenprinting.

Recording electrode 11 expands from voltage supply part (not shown), inthe root in FIG. 1(a), and forms one of the walls of the ink channelwith shroud 108 and upside insulating member 13. Ink is supplied fromentrance 16, as indicated by the arrow, and it is collected from exit17. The shape of the entrance 16 and the exit 17 is like a slit, asshown in the d-d′ section (FIG. 3).

The point of recording electrode 11 projects from the edge of thesubstrate 10 toward common electrode 6, as explained with reference toFIG. 2. Here, because ink is supplied to the recording electrode 11, themetal layer of about 1 μm thick is provided on dielectric substance 101,which is about 20 μm thick, to give strength which can resist the weightof ink, and the voltage is applied to this. Further, recording electrode11 is covered by a coating material, such as insulation protection films105. The electric discharge occurs easily from the recording electrode11 when the amount of ink supply to the point of the recording electrode11 decreases for some reason. Therefore, this protection film isprovided to prevent breakage of the point of the recording electrode 11by the electrical discharge.

When the ink is supplied or is collected as above-mentioned, an inkmeniscus is formed in the vicinity of the point of recording electrode11. FIG. 12 shows the state in which the ink meniscus is formed in thesame section as FIG. 1. Further, FIG. 13 shows the ink meniscus as seenfrom the upper direction of the ink discharge part. The ink meniscus 18is formed in a shape by which ink is supplied to the point of therecording electrode. When the pulse voltage is superimposed on theelectrode bias at the time of recording, ink drop 30 in an amountcorresponding to the applied time of the pulse voltage is dischargedtoward recording medium 7. When the weight ratio of the insolublematerial which contains pigments included in said ink drop is more thanthe weight ratio of the solvent, a stable discharge of the ink dropbecomes difficult as the applied period of the pulse voltage isincreased from about 1 kHz to about 10 kHz. Therefore, it is preferablethat the weight ratio of said insoluble material included in the inkdrop is lower than that of the solvent.

Further, a proper range (corresponding to the thickness of dielectricsubstance sheet 108) exists in the height of the ink channel in FIG.1(a). About 70-150 μm is preferable for this height. The reason for thisis that enough ink cannot be supplied to the point of the recordingelectrode 11 due to an increase in the ink channel resistance when theheight of the ink channel is too low. On the contrary, the point ofrecording electrode 11 shifts downward due to the weight of the ink whenthe ink channel is too high, so that the impact position of the ink onthe recording medium is displaced. Thus, it is possible to prevent thepotential of each recording electrode 11 from being transmitted to theadjacent recording electrode 11 through the ink by individuallyproviding an ink channel for every recording electrode. Therefore, theelectric field distribution of each channel can be stabilized. However,because an ink meniscus is formed at the point of the recordingelectrode 11, as shown in FIG. 13, the ink meniscus is mechanicallypartitioned by a projecting part of the control electrode 12. And,because the electrode bias is applied to control electrode 12, thevoltage applied to recording electrode 11 will never be transmitted tothe adjacent recording electrodes. Control electrode 12 exists withouttouching the ink directly under the dielectric substance sheet 108, asshown in FIG. 1(b). Further, instead of the method of collecting inkfrom the point of a recording electrode 11, as shown in FIG. 1, it ispossible to collect ink in a direction downward from the point ofrecording electrode 11, as shown in FIG. 7. In that case, it is notrequired to provide ink exit 17 at the upside insulating member 13 inthe ink discharge part. Details of the configuration by which ink iscollected downward will be explained with reference to FIG. 14. If theamount of the projection of the recording electrode 11 is set within theabove-mentioned range, it is possible to select the directions from thehorizon to the right above and from the horizon to the diagonal bottom,because ink is collected by using a pump, though the recording head ofthe present invention is one for recording while circulating ink.Because the interval of the recording electrode 11 becomes about 250 μmwhen the ink discharge part shown in FIG. 1-FIG. 3 is adopted, it isnecessary to arrange recording electrodes 11 in a staggered form bystacking several substrates 10 to achieve a recording head which recordsa high definition image at a high speed.

FIG. 11 shows a section through three substrates 10 piled up in a stack.In the ink jet recorder of the type where the recording head is fixed,the stage number n of a necessary substrate 10 is provided by a desireddot interval d1 when printing and the interval d2 of recording electrode11 which exists on one substrate. Where, d2=d1×n.

The line heads of n stages are piled up so that ink discharge part 5 canbe arranged to shift in a zigzag manner in order that a dot will beprinted at a desired pitch in both the recording medium transportationdirection and the vertical direction. Because, in the ink jet recorderof the type in which printing it carried out as the recording head ismoving, the recorder with larger stage number n has an improved theprinting speed and definition, so that the stage number n is based onthe specification of the recorder.

One example of the method of manufacturing the above-mentioned inkdischarge portion will be explained next with reference to FIG.8(a)-FIG. 10(e), which show crosssections of the recording electrode asseen from the point side. FIGS. 8(a)(1) respectively shows a top viewthereof.

As seen in 8(a), first of all, groove 100 is formed in substrate 10,such as a glass substrate of about 1 mm in thickness by using a dicingsaw. The width L2 of this groove 100 is 0.2-0.5 mm, and the depth L1 isabout 0.2 mm. However, it is necessary to increase the length L3morethan the width, when it is used as a recording head.

As seen in FIG. 8(b), a dielectric polyimide sheet 101 of about 20 μmthick is provided on substrate 10 by thermocompression bonding, and ametallic film 102 about 1 μm thick is formed by a sputtering method,etc.

As seen in FIG. 8(c), a photoresist is spread on the metallic film 102,and the photoresist layer is exposed through a photomask which has afixed electrode pattern. And, the photoresist pattern is formed onmetallic film 102 by development. The recording electrodes 11 andcontrol electrodes 12 are formed from the etching of a metallic film 102by using this photoresist pattern as a mask.

As seen in FIG. 8(d), polyimide 105, which forms an insulationprotection film, is spread by spin coating and is solidified. As aresult, a film having a thickness of 5 μm level is formed. In addition,a metallic film 106 about 1 μm thick is formed thereon by a sputteringtechnique etc.

As seen in FIG. 8(e), a photoresist is spread on metallic film 106, andthe photoresist layer is exposed through a photomask which has a fixedelectrode pattern. And, the photoresist pattern is formed on metallicfilm 106 by development. A desired electrode pattern 107 is formed fromthe etching of metallic film 106 by using this photoresist pattern as amask. This electrode pattern 107 is wider by about 5 μm than the patternof the recording electrodes 11.

As seen in FIG. 9(a), a dielectric polyimide sheet 108 about 70-100 μmthick is formed on the electrode pattern 107 by thermocompressionbonding. In addition, metal film 109 about 2 μm thick is formed on that.A different metallic film from metallic film 106 is used as metallicfilm 109. The reason for this is that selection etching is needed in thepost-processing of this method of manufacture.

As seen in FIG. 9(b), a metallic film pattern 110 and themetal-dissolved space 111 are formed next by using photo-lithography andetching like the above-mentioned process.

As seen in FIG. 9(c), space 112 which serves as an ink channel is formedby dry-etching the polyimide layer 108 by using metallic pattern 110,107as a mask, and the point protruding portions of the recording electrodes11 and control electrodes 12 are formed at the same time.

As seen in FIG. 9(d), only metallic pattern 110 is removed by a wetetching.

As seen in FIG. 10(a), polyimide sheet 13 about 20 μm thick is formed onpolyimide layer 108 by thermocompression bonding, and a metallic film114 about 1 μm thick is formed on that. Here, the same material as usedmetallic film 107 may be used as metallic film 114.

As seen in FIG. 10(b)(1), a metallic film pattern 115 is formed by photolithography and etching similar to the above-mentioned process.

As seen in FIG. 10(c)(1), polyimide sheet 13 is processed by dry etchingusing this metallic film pattern 115 as a mask.

As seen in FIG. 10(d)(1), metallic films 107 and 114 are removed by wetetching, and an ink entrance 16 and an exit 17 are formed. Exit 17 isunnecessary for the method of ink circulation shown in FIG. 7.

As seen in FIG. 10(e)(1), the groove is formed from the back using adicing saw according to groove 100 on the surface of substrate 10. And,substrate 10 is folded and divided at the bottom in two grooves and thefolded surface is ground diagonally.

The points of recording electrodes 11 and the points of controlelectrodes 12 project suitably from the edge of the substrate 10 as aresult of the above-mentioned process. Finally, cover 19 in which an inkchannel is formed in the upper part of manufactured substrate 10 isprovided. As a result, the ink discharge portion of FIG. 1 is completed.

Between at least adjacent and above-and-below substrates, when the inkdischarge portion of FIG. 11 is manufactured, substrates 10 having acover 19 are accumulated, with the position of the recording electrodes11 being displaced in an inplane direction.

FIG. 14, FIG. 15, and FIG. 16 show the configuration in which ink iscollected from the points of recording electrodes 11 shown in FIG. 7downward. These figures are the schematic diagrams of the ink dischargeportion of the ink jet recorder according to another embodiment of thepresent invention. FIG. 14 shows an upper sectional view of the inkdischarge portion, FIG. 15 shows a section taken on line a-a′ in FIG.14, and FIG. 16 shows a section taken on line b-b′ in FIG. 15.

Recording electrodes 11 and control electrodes 12 are formed bydepositing a metallic film and wet-etching using photo lithography afterthe thermocompression-bonding of a resin film 101 (for instance,negative type exposure resin film) of a low dielectric substance(specific inductive capacity is 3 or less) on a glass substrate 10.Point portions 11-1 of the recording electrodes project from the endface of glass substrate 10 and have a sharp angle. Further, they arearranged in parallel at a constant interval as shown in FIG. 14. Inaddition, the recording electrodes 11 and control electrodes 12 arecovered by an insulation protection film 105.

On the other hand, point portion 12-1 of the control electrode is behindpoint portion 11-1 of the recording electrode and projects from the endface of glass substrate 10. Each control electrode 12 is arrangedbetween recording electrodes 11 at a constant interval.

In addition, a migration electrode 20-1, which has the same length asthe width of a row of recording electrodes 11 or more, is arranged atthe rear on the opposite side with respect point portions 11-1 of therecording electrodes, and it is right-angled with respect to thedirection of recording electrodes 11. Migration power supply 20 isconnected to said migration electrode 20-1. There is an effect in thatthe amount in which the particles of electrification pigments includedin ink gather toward points 11-1 of the recording electrodes isincreased by raising the voltage applied from migration power supply 20to a level higher than the electrode bias applied from bias supply 15.However, migration electrode 20-1 is not necessarily used for thispurpose. When the printing speed is increased, and the particles ofelectrification pigments supplied to point portion 11-1 of the recordingelectrode is increased, this electrode is effective.

Point portion 12-1 of the control electrode serves to separate the inkmeniscus between adjacent recording electrodes 11 mechanically by beingcovered with a low dielectric resin film 101 on an insulation protectionfilm 105 and projecting. In addition, high resolution picture printingwith few differences in the size of the flight of the ink drop and thebending of the flight of the ink drop due to the influence betweenadjacent recording electrodes 11 is made possible by intercepting theinterference due to the electric field between adjacent recordingelectrodes 11. It is preferable to set the height s of the point of thecontrol electrode to the same height h as an ink channel or more, inorder to make the effect by which the ink meniscus between adjacentrecording electrodes 11 is mechanically separated more effective.

The point of the metallic control electrode is covered by a layer whichis configured of a resin of a dielectric substance in the portion whereit projects from the end face of the glass substrate 10. Of course, asimilar effect can be obtained even if a similar shape is configuredonly of the metallic control electrode.

Ink supply channel 34 in the ink discharge portion 5 is formed, alongthe upper side of recording electrode 11, by working resin film 108 (forinstance, a negative type photosensitive resin film) of a low dielectricsubstance thermocompression-bonded on insulation protection film 105 bya wet etching using lithography, as shown in FIG. 15 and FIG. 16. Inksupply channel 34 in the recording head is worked deeper, with a highdegree of accuracy and in a short time, by adopting the wet etchingprocessing method compared with the above-mentioned dry etchingprocessing method.

Next, resin film 13 formed of a low dielectric substance (for instance,negative type resist resin film) is put on ink supply channel 34, saiddielectric substance resin film 108 is thermocompression bonded to sealthe ink supply channel 34, and then ink supply port 16 is processed bywet etching. In addition, cover 19 is bonded on low dielectric resinfilm 13. As a result, supplying ink 26 to ink supply channel 34 becomespossible.

As shown in FIG. 14, ink supply channel 34 is formed along recordingelectrode 11, ink 26 is supplied in the direction designated by thearrow, and said supply ink flows toward point the portion 11-1 of therecording electrode.

FIG. 14 and FIG. 16 each shows the configuration in which threerecording electrodes 11 and four control electrodes 12 are illustratedas a matter of convenience. However, the number of these recordingelectrodes 11 and control electrodes 12 can be increased from dozens toseveral thousands according to the usage of the ink jet recorder in asimilar manner, by alternately arranging recording electrodes 11 andcontrol electrodes 12 and providing control electrodes 12 at both endsof the recording head. Therefore, it is needless to say that it ispossible to produce a multi-channel type recording head and a line typerecording head.

Here, an electrode bias is applied from bias supply 15 to each recordingelectrode 11, and the pulse voltage from the pulse voltage generationcircuit 14 is superimposed on the bias voltage applied to recordingelectrode 11 to make the ink fly. In addition, ink 26 is made bydistributing a coloring material or pigments in a solvent of thepetroleum oil group, such as isoparafin, or a solvent of silicon group,with a dispersing agent and an electrification control agent, etc., andmaking positive-electrified pigment particles. Additionally, thedetailed content of the ink is as explained with reference to FIG. 4.Therefore, an electric field is formed between grounded common electrode6, and recording medium 7 disposed on said common electrode 6, and pointportion 11-1 of said recording electrodes by applying the electrode biasfrom bias supply 15 in FIG. 14, whereby positively electrified pigmentparticles are collected point 11-1 of the recording electrode, wherethey are concentrated. Then, concentrated ink drop 30 is allowed to flytoward recording medium 7 by applying a pulse voltage from the pulsevoltage generation circuit 14. Migration electrode 20-1 is provided oncover 19, which consists of a dielectric substance, in the rear of therecording electrode as shown in FIG. 15. Here, when the weight ratio ofthe insoluble material which contains pigments included in said ink dropis more than the weight ratio of the solvent, a stable discharge of inkdrops becomes difficult as the period of the application of the pulsevoltage is increased from about 1 kHz to about 10 kHz, in addition tothe effects described with reference to in FIG. 1. Therefore, it ispreferable that the weight ratio of said insoluble material included inink drops is less than that of the solvent.

Next, the configuration by which the residual ink quantity is determinedafter the ink is collected will be explained with reference to FIG. 15and FIG. 16. Minute space 35 with a constant size g is provided betweenink collection member 36 and point portion 10-1 of the glass substratehaving a slope near the point of the recording electrode. In addition,an airflow is applied to ink collection member 36 and ink collectionchannel 37, formed by the portion of glass substrate 10 which has aslope, in order to collect said residual ink quantity under point 11-1of the recording electrode and at a certain angle which intersects thedirection of point 11-1 of the recording electrode. The residual inkquantity mixes with the above-mentioned airflow and is collected at highspeed. Therefore, by collecting the air around ink meniscus formedaround the recording electrode and the control electrode and drawing itinto the ink collection channel through a minute space, an airflow isgenerated around the ink meniscus, and thus a suitable ink meniscus forink discharge is formed. Especially, the range of 100 μm-500 μm wasfound to be effective as the size g of the channel of said minute space35. The shape of the ink meniscus 18 in FIG. 17 and FIG. 18, to bedescribed later, did not form an ideal concave in 500 μm or more, and in100 μm or less, and the shape of above-mentioned ink meniscus 18 was notsteady.

Here, the pressure of point portion 11-1 of each of the plurality ofrecording electrodes (negative pressure) and the amount of inkcollection can be evened up by widening the shape of the ink collectionmember 36 at the point portion 11-1 side of the plurality of recordingelectrodes, and narrowing it as it becomes further from the points ofthe recording electrodes, as shown in FIG. 16. The effective angle θ wasfound to be from 30 to 120°. The size of the ink collection member 36was large compared with the length of the recording head (length of thedirection of a row of said recording electrodes) at 30° or less, andsaid pressure (negative pressure) and the amount of ink collection wasnot able to be evened up at 120° or more.

The pigments included in said ink can be prevented from adhering byinstalling a film (not shown) of ink material in the ink collectionchannel 37 of the ink collection member 36 and in the minute space 35 asseen in FIG. 15 and FIG. 16. In addition, it is possible to obtain aconfiguration in which the variation per hour of the ink meniscus 18shown in FIG. 17 and FIG. 18 is small, and the ink circulation system isstable.

It is needless to say that a similar effect can be obtained even if thepoint portion 11-1 side of plural recording electrodes is widened, andthe collection ink outflow entrance 54 side is formed so as to have anarrow curved surface, though the shape of the ink collection member 36is shown to have a V-letter form in FIG. 16.

FIG. 19 is a schematic diagram of the recording head, which includes theink circulation portion of the ink jet recorder according to oneembodiment of the present invention. Here, the example of the inkdischarge portion 5 is the same as the embodiment of FIG. 14, FIG. 15,and FIG. 16. Common electrode 6 is opposed to the ink discharge portion5, and the recording medium 7 is in contact with common electrode 6 asshown in FIG. 19. In addition, ink 26 is supplied to ink dischargeportion 5 via ink supply pipe 23 e and 23 a by pump 22, and ink iscollected via ink collection tube 23 c. The common electrode 6 isgrounded, and an electrode bias of about 0.5 kV-3 kV is applied to inkdischarge portion 5 by bias supply 15. In addition, a pulse voltage ofabout 0.2 kV-1 kV is superimposed on the electrode bias applied to theelectrode by pulse voltage generation circuit 14 according to the recordsignal. An ink drop 30 is caused to fly from the point of ink dischargeportion 5 toward recording medium 7 due to the electrostatic fieldformed between the ink discharge portion 5 and common electrode 6, withwhich the recording medium 7 is in contact. High resolution picturerecording becomes possible because the size of the ink drop 30 can befreely changed in proportion to the pulse width of the pulse voltage 14.

The minute particles of positively electrified pigment are collectedalong point 11-1 of the recording electrode, by distributing thepigments in a solvent of a petroleum oil group, such as isoparafin, or asolvent of a silicon group, with a dispersing agent and anelectrification control agent, to produce positive-electrified minuteparticles, which are concentrated. Therefore, the concentration of inkdrop 30 is improved more than pigment concentrations of ink suppliedfrom the ink supply pipe 23 a. A blur of ink on the recording medium 7,which occurs in the conventional ink jet recorder can be reduced, and itbecomes possible to obtain a high resolution picture. In addition, therecording medium which can be used is not limited, so that convenienceand low-cost use become possible.

It is necessary to make the amount of ink 26 supplied to the inkdischarge portion 5 and its supply pressure (positive pressure), and theamount of ink 26 collected from the ink discharge portion and itscollection pressures (negative pressure) constant, and it is necessaryto circulate ink at high speed in order to fly a stable ink drop 30 athigh frequency in the ink jet recording method which has such variousfeatures. To keep the amount of the ink supplied to the ink dischargeportion 5 and its supply pressure (positive pressure) constant, theamount of ink supply and the supply pressure of pump 22 should be keptconstant. It is necessary to enlarge the sectional area of ink supplychannel (34 in above-mentioned FIG. 15) in ink discharge portion 5 tomake ink circulate at high speed.

Next, air is sucked by a suction mechanism (by using suction tube 23 fand vacuum pump 27 in this embodiment) which sucks air from air layer 25in the ink collection container 21, which is sealed up, and dischargesit into the atmosphere as exhaust 28 to keep the amount of the ink 26collected from the ink discharge portion 5 and its collection pressure(negative pressure) constant. The space occupied by air layer 25 is at anegative pressure because ink collection container 21 is a sealedstructure. Surplus ink is collected from the point of ink dischargeportion 5 to ink collection container 21 with air via piping 23 c, whichcommunicates with the space containing air layer 25 of negativepressure. The mixture of air and surplus ink collected in the air layer25 in ink collection container 21 is separated by the specific gravitydifference between the air and ink in the air layer 25. The separatedink merges into collected ink 26, and air is discharged into atmosphereby vacuum pump 27 as exhaust 28 via suction tube 23 f. The amount of thecollection of ink 26 collected from ink discharge portion 5 and itscollection pressure (negative pressure) can be kept constant by settingthe suction force of said vacuum pump 27.

The pressure of air layer 25 can be changed and the shape of the inkmeniscus shown in FIG. 17 and FIG. 18 can be controlled by controllingthe airflow control valve 51 according to an instruction from a flowcontrol circuit 52, thereby adjusting the amount of the airflow whichflows in suction tube 23 f and the flow velocity. Ink 26 in inkcollection container 21 is drawn up by pump 22 via piping 23 e, and itis supplied to ink discharge portion 5 via piping 23 a.

Details of the separation of ink and air in the ink collection container21 in FIG. 19 is shown in FIG. 20. The inside of said ink collectioncontainer 21 is sealed by container lid 21-A. Further, the inkcollection container 21 has a two layer structure. Collection ink layer26, where the specific gravity is high, is formed in the lower part ofthe container. Further, an air layer 25, where the specific gravity islow, is formed in the upper part above the collection ink layer 26. Airis sucked from the air layer 25 by vacuum pump 27 through air suctiontube 23 f inserted in air layer 25, and sucked air 28 is exhausted tothe atmosphere. As a result, air layer 25 is decompressed to a negativepressure, and the mixture of the air and the surplus ink is sucked frompiping 23 c into the air layer 25 in the ink collection container 21.Ink particles 26-1 having a high specific gravity drop due to thedifference in the specific gravity after the mixture is sucked into airlayer 25, and these ink particles are absorbed into the ink layer 26.Air with low specific gravity stays in the air layer 25, and it isexhausted to the atmosphere by vacuum pump 27 through air suction tube23 f. As a result, the pressure of the air layer 25 (negative pressure)is always kept constant. It is possible to exhaust clean air to theatmosphere by using a filter 38. Ink is drawn up by piping 23 e insertedin the collection ink layer 26.

FIG. 21 and FIG. 22 show an embodiment of an ink discharge portion inthe ink jet recorder of the present invention, wherein a plurality ofink discharge parts are stacked is piled. FIG. 22 shows a section takenalong line c-c′ in FIG. 21.

By changing only the ink collection member 36 in the ink dischargeportion 5 in the embodiment based on FIG. 14 to FIG. 16, and by formingan ink collection channel 37 along the glass substrate 10, as shown inFIG. 21 and FIG. 22, ink discharge portion 5-A, ink discharge portion5-B, and ink discharge portion 5-c are stacked and fixed. In this case,it is important that the position of point 11-1 of each of the recordingelectrodes 11-A, 11-B, and 11-C in each ink discharge portion isadjusted with a high degree of accuracy.

It is necessary to form a position adjustment mark or positionadjustment projection and a position adjustment hole (not shown) the inkdischarge parts 5-A, 5-B, and 5-C in the process of forming a thin filmtherein, in order to minimize the difference in parallelism in top andbottom and right and left directions, and the pitch drift of recordingelectrodes 11-A, 11-B, and 11-C between ink discharge parts, and makethe interval of common electrode 6, recording medium 7, and the point11-1 of said each recording electrode uniform. Ink is supplied toindividual ink supply pipes 23 a-A, 23 a-B, and 23 a-C of the recordinghead that is stacked with a high degree of accuracy through ink supplypipe 23 a.

Further, ink is collected from individual ink collection tubes 23 c-A,23 c-B, and 23 c-C through ink collection tube 23 c. Ink flows from theindividual ink supply pipe toward point portion 11-1 of the recordingelectrode in the ink supply channel 34 via cover 19 by such aconfiguration, and an ink meniscus 18 is formed between point portion11-1 of said recording electrode and point portion 12-1 of said controlelectrode. The unused ink is collected from collection ink outflowentrance 54 to the individual ink collection tube via an ink collectionpassage. This configuration has the same feature as that in theembodiment of FIG. 14 to FIG. 16. In addition, an ink drop can fly fromthe recording electrodes 11-A, 11-B, and 11-C toward common electrode 6and recording medium 7 at the same time. Therefore, making an ink dot ofhigh density, whereby high-speed printing becomes possible.

The left side view of the ink discharge part of FIG. 21 is shown in FIG.23. The pitch between recording electrode 5A-1, 5A-2, and 5A-3 of singleink discharge part A is P1. However, by shifting the positions of thethree ink discharge parts 5-A, 5-B, and 5-C and stacking them in astaggered fashion, that is, by adding recording electrodes 5B-1,5B-2,5B-3 of ink discharge portion 5-B and recording electrodes 5C-1,5C-2,5C-3 of ink discharge portion 5-C, the pitch P2 between therecording electrodes is made one third.

It is necessary to increase the width of the ink supply channel 34 inthe ink discharge portion 5 to secure a sufficient amount of inkcirculation. Making the desired ink dot high density can be achieved bystacking a plurality of ink discharge portions as shown in FIG. 23,although there is a limitation in narrowing the pitch P1 betweenrecording electrodes in a single ink discharge portion.

It is needless to say that it is possible to increase and decrease thenumber of ink discharge portions to be stacked, if necessary, althoughthe provision of three ink discharge portions is shown in thisembodiment.

Further, the control of each ink supply and the collection becomes easy,and the arrangement of parts in the ink jet recording head becomes easyby sharing the supply and the collection of ink in the stacked inkdischarge portions for the multi-steps in the root of a ink dischargeportion.

An example in which the positions of plural ink discharge portions 5-A,5-B, and 5-C are shifted and stacked in a staggered fashion is shown inFIG. 21 and FIG. 23. However, it is possible to print at high speedcompared with the case of single record head by piling ink dischargeportions without shifting them and circulating ink.

Details of the effect obtained by making the pressure of the air layer25 (negative pressure) in the ink collection container 21 shown in FIG.20 constant will be explained with reference to FIG. 17 and FIG. 18.

FIG. 18 shows a partial enlarged side view of the ink discharge portion5, and FIG. 17 shows a section taken along the line d-d′ in FIG. 18.

Constant airflow 50 is generated in the direction designated by thearrow through minute space 35 formed by glass substrate 10 andcollection member 36 according to the constant pressure of the air layer25 shown in FIG. 19 (negative pressure), and the residual ink iscollected with the airflow 50. It is possible to adjust the speed of theairflow and the flow amount by increasing and decreasing the negativepressure of air layer 25 shown in FIG. 19, and it is possible tooptimize the shape of the ink meniscus 18, which encompasses the pointportion 11-1 of the recording electrode 11, so that it is concave alongthe front end part of the glass substrate 10, as shown in FIG. 17. Here,it is important to keep the ink meniscus steady at the time the inkflies. The airflow is controlled by a vacuum pump to stabilize inkmeniscus.

Ink meniscus 18-a and 18-b, seen from the upper surface of the recordinghead in FIG. 18, can be also formed uniformly to have a concave shapealong the front end of the glass substrate 10 to encompass pointportions 11-1 a and 11-1 b of the recording electrodes. Further, the inkmeniscus 18-a and 18-b are interrupted mechanically by point portions12-1 a, 12-1 b, and 12-1 c of the control electrodes. Here, it is to beunderstood that the angle α of the point of said recording electrodegreatly influences the ink flight. When the angle α exceeds 70°, inkflight becomes difficult due to a decrease in the concentration of theelectric field at the point of the recording electrode. When the angle abecomes smaller than 25°, the agglutination of the pigment particles inthe ink is strengthened too much at the point of the recordingelectrode, and the ink flight becomes difficult, although theconcentration of the electric field at the point of the recordingelectrode is improved. Therefore, it is preferable that the angle α iswithin the following ranges.

25°≦α≦70°

Next, it has been determined that the ratio of the thickness t of thepoint to curvature r of the point of said recording electrode greatlyinfluences the ink flight. For example, the concentration of theelectric field on the point of the recording electrode decreases, theink flight becomes difficult and the shape of the ink drop becomes anoval when enlarging t/r, that is, when the point thickness t isincreased, the point curvature r is reduced, and t/r exceeds 6.0. On theother hand, the machine strength of the recording electrode decreases asthe point thickness t is reduced when reducing t/r, that is, when thepoint thickness t is reduced and the point curvature r is enlarged.Therefore, when the point is transformed by external force due to thehigh-speed flow of ink and the point curvature r is enlarged, theconcentration of the electric field on the point of the recordingelectrode is decreased, and stable ink flight becomes difficult, whent/r is 1.0 or less.

As a result, it is preferable that the ratio of point thickness t andpoint curvature r satisfies the following relationship.

1.0≦t/r≦6.0

Next, it has been determined that the ratio of the height h of inkchannel and the projection amount 1 of the control electrode isimportant for a stable ink drop flight. When the mechanical shieldeffect on the ink meniscus by the point of the control electrode becomesinsufficient, the movement of ink to the adjacent recording electrodeside will occur easily, and a stable ink flight becomes difficult, whenenlarging h/1, that is, when the height h of the ink channel isincreased and the projection amount 1 of the recording electrode isreduced. On the other hand, when reducing h/1, that is, when the heighth of the ink channel is lowered, and the projection amount 1 of thecontrol electrode is enlarged, the ink was not supplied easily to thepoint of the recording electrode, the concentration of the electricfield on the point of the recording electrode was decreased, and astable ink flight became difficult.

Therefore, it is preferable that h/1 satisfies the followingrelationship.

5≦h/1≦8.0

Next, it has been determined that the ratio of the height h of the inkchannel and the width w of the ink channel, as shown in FIG. 16, isimportant for proper ink flight. When enlarging h/w, that is, when theheight of the ink channel is enlarged, the width of the ink channel isreduced, and h/w exceeded 2.0, the manufacture of the channel wasdifficult. When reducing h/w, that is, when the height of the inkchannel is reduced, the width of the ink channel is enlarged, and h/wfalls below 0.5, the supply of ink to the point of the recordingelectrode was difficult, and stable ink flight was difficult.

Therefore, it is preferable that h/w satisfies the followingrelationship.

0.5≦h/w≦2.0

Next, it has been determined that the ratio of projection amount 1 ofthe point of said control electrode and the projection amount L of thepoint of said recording electrode is important for a stable ink flight.When enlarging 1/L, that is, when the projection amount 1 of the controlelectrode was enlarged, the projection amount L of the recordingelectrode was reduced, and 1/L became more than 0.4, ink dischargebecame difficult due to the decrease of the concentration of theelectric field on the point of the recording electrode. When reducing1/L, that is, when the projection amount 1 of the control electrode wasreduced, the projection amount L of the recording electrode wasenlarged, and 1/L became smaller than 0.1, the mechanical interruptionof said ink meniscus by the control electrode point became insufficient,ink got over the point of said control electrode and flowed out to thepoint of the adjacent recording electrode, and stable ink dischargebecame difficult.

Therefore, it is preferable that the relation of the amount L of theprojection of the point of the recording electrode to the projectionamount 1 of said control electrode point is as follows.

0.1≦1/L≦0.4

The concentration of the electrostatic field formed according to thedischarge electrode point form and ink meniscus form becomes strong byoptimizing the ink meniscus form. As a result, ink can fly stably towardthe common electrode 6 and recording medium 7 even if the electrode biasand the pulse voltage are lowered. Especially, the economical effect isremarkable because the pulse voltage generated by pulse voltagegeneration circuit 14 can be lowered, so that low voltage drive becomespossible, and the adoption of a general-purpose driving IC becomespossible.

In addition, the size of the ink drops can be equalized by keeping theshape of the ink meniscus of each discharge electrode point constant,and the possibility of producing a high resolution picture is alsoextremely large.

FIG. 24 is a schematic diagram of the ink jet recording head whichincludes the ink circulation part according to one embodiment of thepresent invention, in which the function is added to the configurationof the embodiment in FIG. 19. Common electrode 6, which is opposed tothe ink discharge portion 5 and is in contact with recording medium 7,is arranged as shown in FIG. 24. In this embodiment, ink 26 is suppliedto ink discharge portion 5 via ink supply passage 23 b, and ink 26 iscollected via ink collection passage 23 c.

To keep the ink supply and the ink supply pressure (positive pressure)constant, the liquid level of ink 26 in ink flow modulating compartment24 and the head H of the recording head should be kept constant.Therefore, an overflow ink collection passage 23 g is provided betweenink flow modulating compartment 24 and ink collection container 21, andink within a range which exceeds the top of overflow ink collectionpassage 23 g is collected in ink collection container 21. As a result,the head H can be kept substantially constant anytime. Thus, theconfiguration shown in FIG. 5 may be used for keeping the head Hconstant. It is necessary not only to raise the head H, but also toenlarge the sectional area of the ink supply passage in the inkdischarge portion 5 to circulate ink at high-speed. However, it ispossible to make the ink circulate at high speed by using the inkdischarge portion shown in the above-mentioned FIG. 14, FIG. 15, andFIG. 16.

Next, air in the ink collection container 21 is sucked by vacuum pump 27through air suction tube 23 f and is discharged into the atmosphere asexhaust 28 to keep the amount of ink and the collection pressure(negative pressure) in container 21 constant. Air layer 25 becomes anegative pressure in the ink collection container 21, which is a sealedstructure. Surplus ink is collected in the ink collection container 21via ink collection passage 23 c which extends into air layer 25 ofnegative pressure. The amount of ink and its collection pressure(negative pressure) can be kept constant by setting the suction ofvacuum pump 27.

Collection ink 26 in ink collection container 21 is drawn up by liquidpump 22 via ink supply pipe 23 e, and it is dispensed into filter 31 viaink supply pipe 23 a. Any foreign bodies in the ink 26 are filtered byfilter 31 and collected in the ink modulating flow compartment 24.

In addition, ink and solvent switching valve 43 is provided in the inksupply pipe 23 b to switch to either the supply of ink 26 in the inkmodulating flow compartment 24 or the supply of solvent in the solventsupply container 41. Ink 26 in the ink modulating flow compartment 24 issupplied to the ink discharge portion 5 to provide the ink which formsthe concentrated ink drop 30 when an image is printed. When imageprinting stops, the solvent in the solvent supply container 41 can besupplied, whereby the ink passages of the ink discharge portion 5, theink supply pipe 23 b, and the ink collection tube 23 c are cleaned. As aresult, in the ink circulation part the amount of ink circulation isprevented from changing due to pigments in the ink clinging in the inkpassage, so that a high reliability can be obtained. It is possible tomaintain the pigment concentration of the ink in the ink collectioncontainer within a fixed range by opening the concentrated ink supplyvalve 44 and supplying concentrated ink in the ink replenishmentcontainer 42 to the ink collection container 21. To prevent ink pigmentsfrom settling and to maintain the ink uniformity, a stir mechanism 45 isprovided in the ink collection container 21. In addition, to subject theink to atmospheric pressure, that is, to the solvent, air vent 33 isprovided in the upper part of ink modulating flow compartment 24, inkreplenishment container 42 and solvent supply container 41.

It is preferable that ink replenishment container 42 and solvent supplycontainer 41 are cartridges that are able to be detached.

An embodiment which is directed to the protection of the point of therecording electrode according to the present invention is shown in FIG.25. Protection protruding portion 36-1 on ink collection member 36 andprotection protruding portion 19-1 on the cover 19 project from point10-1 of the glass substrate. By increasing the height of the projectionof said protruding portion so that it extends further than point 11-1(dielectric substance resin film 101 and insulation protection film 105are included) of the recording electrode, protection protruding portions36-1 and 19-1 can support the recording medium when recording medium 7approaches point 11-1 of the recording electrode at the time of imagerecording. As a result, recording medium can be prevented from cominginto contact and damaging point 11-1 of the recording electrode.

In addition, ink pocket 40, which encompasses point 11-1 of therecording electrode, is formed by protection protruding portion 36-1,protection protruding portion 19-1, and glass substrate point 10-1. Inkpocket 40, which encompasses point 11-1 of the recording electrode, issealed by bumping capping material 39 against said protection protrudingportions when image recording stops so as to stop the collection of inkfrom ink collection channel 37. On the other hand, ink supply channel 34supplies ink 26 to ink pocket 40 to fill it with ink. As a result, theink on point 11-1 of the recording electrode is prevented from drying.Accordingly, changes in the ink drop discharged from the point of saidrecording electrode due to pigment particles included in the ink beingstuck to point 11-1 of the recording electrode can be reduced, so thatan image recorder in which the reliability is extremely high can beobtained. It is more effective when a soft elastic body (not shown) isprovided to seal up the part of the capping material 39 that contactssaid protection protruding portion 36-1, 19-1, so as to prevent inkleakage, or when the capping material 39 is formed with a soft elasticbody.

Another embodiment of the ink jet recording head according to thepresent invention, having an ink discharge portion that is differentfrom that of FIG. 19, is shown in FIG. 26.

Ink discharge portion 5 forms an ink meniscus 18 by using aconfiguration in which a plurality of recording electrodes 11 arearranged on both sides of a projecting board 53, which has a pluralityof sharp points made of a dielectric substance, an ink supply pipe 23 ais connected to an ink supply channel 34 which is sandwiched byprojecting board 53 and recording electrode 11, and ink is supplied tothe point of the recording electrode 11 and the point of the projectingboard 53. An ink drop 30 is discharged from the point of projectingboard 53 toward common electrode 6 and recording medium 7 by applying apulse voltage from the pulse voltage control circuit 14 and an electrodebias from bias supply 15 to recording electrode 11. The remaining ink iscollected in the direction designated by the arrows with the airflowproduced by the negative pressure of air layer 25 in ink collectioncontainer 21 by connecting collection tube 23 c to ink collectionchannel 37. Air suction tube 23 f is inserted into the air layer 25, airis sucked by vacuum pump 27, and sucked air is exhausted to atmosphereas exhaust 28. The ink and the air which entered air layer 25 throughink collection tube 23 c are separated in the air layer 25, and theseparated ink enters the ink layer 26. Collected ink 26 is supplied toink supply channel 34 by pump 22 through tube 23 e and the tube 23 a.The air flow rate and the flow velocity which flows in suction tube 23 fcan be adjusted by controlling the flow control valve 51 according to aninstruction received from the flow control circuit 52. As a result, itis possible to control the ink meniscus 18 to have a shape suitable forthe flight of the ink drop 30. In the ink jet recording head having theconfiguration of FIG. 26, the shape of ink meniscus 18 can be controlledby the airflow, so that the ink drop 30 can fly even if the pulsevoltage applied by pulse voltage generation circuit 14 is reduced to alow voltage, whereby the ink drop 30 can be made uniform.

In addition, the ink circulation velocity of the ink discharge portion 5can be increased because the air layer 25 is at a negative pressure andink is collected compulsorily with the airflow, so that the ink can flowsteadily even if the frequency of generation of the ink drops 30 isincreased. As a result, the printing speed of the ink jet recorder canbe made high-speed.

As described above, in the ink jet recording head according to thepresent invention, the impact position of ink at the time of printingcan be prevented from shifting, so that an ink jet recording head whichproduces a high definition image can be provided.

Further, an ink jet recording head in which the shape of a lot of inkdischarge parts can be easily arranged to form a line head is achieved,and a recording head that can be manufactured cheaply and easily can beprovided.

Further, an ink jet recording head which can operate with a low drivevoltage and make the amount of the ink flight uniform can be provided.

Further, a ink jet recording head which can print at high speed can beprovided.

As mentioned above, an ink jet recording head or an ink jet recorderaccording to the present invention is useful for recording a highlyaccurate picture and the character, etc. by ink flight, and it issuitable for use in a color ink jet printer which records using variousmedia.

What is claimed is:
 1. An ink jet recording head comprising: asubstrate, a plurality of recording electrodes arranged on saidsubstrate, a plurality of control electrodes arranged so as to sandwicheach of said recording electrodes, an ink circulation part for supplyingink which contains coloring material in solvent to said recordingelectrodes to flow it in a direction of length of said each recordingelectrode, and collecting said ink from a point of said each recordingelectrode.
 2. The ink jet recording head according to claim 1, wherein ashroud of a dielectric substance is provided between said each recordingelectrode and said each control electrode, and between said each controlelectrode and an ink channel.
 3. The ink jet recording head according toclaim 1, wherein said each recording electrode projects from the edge ofsaid substrate.
 4. The ink jet recording head according to claim 3,wherein said each control electrode project from the edge of saidsubstrate, and the projection amount of said each control electrode issmaller than that of said each recording electrode.
 5. The ink jetrecording head according to any one of claims 1 to 4, wherein said eachrecording electrode is covered by the insulation coating material. 6.Ink jet recording head according to claim 1, wherein an angle θ of saidink collection channel is in the following ranges 30°≦θ≦120°.
 7. The inkjet recording head according to claim 1, wherein height s of the pointof said control electrode is equal to or more than height h of the inkchannel.
 8. An ink jet recording head comprising: a substrate, aplurality of recording electrodes arranged on said substrate, aplurality of control electrodes arranged so as to sandwich each of saidrecording electrodes, and an ink circulation part having ink supplychannel provided to flow ink which contains coloring material in solventto said recording electrodes in a direction of length of said eachrecording electrode, and ink collection channel for collecting the inkfrom a point of said each recording electrode that said ink isdischarged to the lower side of said each recording electrode, whereinthe shape of ink meniscus formed in the vicinity of the point of saideach recording electrode is controlled by giving the airflow directly tosaid ink meniscus.
 9. An ink jet recording head comprising: a substrate,a plurality of recording electrodes arranged on said substrate, aplurality of control electrodes arranged so as to sandwich each of saidrecording electrodes, and an ink circulation part having ink supplychannel provided to flow ink which contains coloring material in solventto said recording electrodes in a direction of length of said eachrecording electrode, and ink collection channel for collecting the inkfrom a point of said each recording electrode that said ink isdischarged to the lower side of said each recording electrode, whereinsaid ink collection channel passes air with ink which flows from thevicinity of the point of said each recording electrode.
 10. The ink jetrecording head according to claim 8 or 9, further comprising: amigration electrode provided at a rear end where ink of said eachrecording electrode is supplied, for increasing an amount of saidcoloring material in ink collected in the point of said each recordingelectrode.
 11. The ink jet recording head according to claim 8 or 9,wherein an angle α of the point of said each recording electrode isformed within the following ranges 25≦α≦70°.
 12. The ink jet recordinghead according to claim 8 or 9, further comprising a plurality of inkdischarge parts at least including said plural recording electrodes andsaid plural control electrodes, and wherein each of said plural inkdischarge parts is arranged with being overlapped like a zigzag, and theink supply and the ink collection for said plural recording electrodeare shared.
 13. The ink jet recording head according to claim 8 or 9,further comprising a capping member for covering said plural recordingelectrodes, and ink holder formed between said capping member and thepoint of said each recording electrode.
 14. The ink jet recording headaccording to claim 8 or 9, further comprising an ink container connectedwith said ink collection channel, having an ink layer for the inkcollected from said ink collection channel and an air layer for air, andwherein the ink is collected by decompressing the air layer in said inkcontainer.
 15. The ink jet recording head according to claim 14, furthercomprising a vacuum pump connected to said ink container, fordecompressing said air layer.
 16. The ink jet recording head accordingto claim 8 or 9, wherein said ink collection channel has a space on theside near the point of said each recording electrode, and narrows at acertain angle as it becomes far from the point of said each recordingelectrode.
 17. The ink jet recording head according to claim 8 or 9,wherein a ratio of height h and width w of said ink supply channelsatisfies the following relationship 0.5≦h/w≦2.0.
 18. The ink jetrecording head according to claim 8 or 9, wherein a ratio of height h ofsaid ink supply channel and projection amount 1 of said controlelectrode from said substrate satisfies the following relationship0.4≦h/1≦1.0.
 19. The ink jet recording head according to claim 8 or 9,wherein a ratio of point thickness t and point curvature r of saidrecording electrode satisfies the following relationship 1.0≦t/r≦6.0.20. The ink jet recording head according to claim 8 or 9, wherein aratio of projection amount I of said control electrode from saidsubstrate and projection amount L of said recording electrode from saidsubstrate satisfies the following relationship 0.1≦I/L≦0.4.
 21. The inkjet recording head according to any one of claims 1, 8 and 9, whereinthe electrical resistivity of said ink is 10⁷ Ω·cm or more, the surfacetension 30 mN/m or less, the viscosity 1-10 mpa·s, the mean particlesize of coloring material 50-500 nm, the surface density of charges ofthe coloring material 1-100 μC/m², and the content of coloring materialparticles 1-10 percent by weight.
 22. The ink jet recording headaccording to claim 21, wherein pigments are used as the coloringmaterial.
 23. The ink jet recording head according to claim 21, whereinisopar is used as the solvent.
 24. The ink jet recording head accordingto claim 21, wherein silicone oil is used as the solvent.
 25. An ink jetrecording head comprising: a substrate, a plurality of recordingelectrodes arranged on said substrate, a plurality of control electrodesarranged so as to sandwich each of said recording electrodes, and an inkcirculation part having ink supply channel provided to flow ink whichcontains coloring material in solvent to said recording electrodes in adirection of length of said each recording electrode, ink collectionchannel for collecting the ink from a point of said each recordingelectrode that said ink is discharged to the lower side of said eachrecording electrode, and ink flow modulating room for modulating anamount of the ink flow to said each recording electrode through said inksupply channel, and wherein said ink collection channel passes air withink which flows from the vicinity of the point of said each recordingelectrode, and the ink from said ink flow modulating room to said pluralrecording electrodes is supplied according to a head difference by aposition where said ink flow modulating room and said plural recordingelectrodes are arranged.
 26. The ink jet recording head according toclaim 25, further comprising an ink replenishment container connectedwith said ink container, for storing ink thicker than ink concentrationin said ink container, and a concentration ink adjustment part foradjusting the supply of thick ink from said ink replenishment containerto said ink container.
 27. An ink jet recording head comprising: asubstrate, a plurality of recording electrodes arranged on saidsubstrate, a plurality of control electrodes arranged so as to sandwicheach of said recording electrodes, and an ink circulation part havingink supply channel provided to flow ink which contains coloring materialin solvent to said recording electrodes in a direction of length of saideach recording electrode, and ink collection channel for collecting theink from a point of said each recording electrode that said ink isdischarged to a lower side of said each recording electrode along a partof said substrate, wherein said ink collection channel has a spaceprovided with respect to said substrate to flow the ink and the aircollected from said each recording electrode, and said space g is withinthe following range 100 μm≦g≦500 μm.
 28. An ink jet recording headcomprising: a plurality of recording electrodes arranged on a substrate,a plurality of control electrodes arranged so as to sandwich each ofsaid recording electrodes, and an ink circulation part having ink supplychannel provided to flow ink which contains coloring material in solventto said recording electrodes in a direction of length of said eachrecording electrode, ink collection channel for collecting the ink froma point of said each recording electrode that said ink is discharged toa lower side of said each recording electrode, and ink flow modulatingroom for modulating an amount of the ink flow to said each recordingelectrode, and wherein a weight % of an insoluble material whichincludes the coloring material contained in an ink drop discharged fromthe point of said recording electrode is less than a weight % of thesolvent.
 29. An ink jet recording head comprising: a plurality ofrecording electrodes arranged on a substrate, a plurality of controlelectrodes arranged so as to sandwich each of said recording electrodes,an ink circulation part having ink supply channel provided to flow inkwhich contains coloring material in solvent to said recording electrodesin a direction of length of said each recording electrode, inkcollection channel for collecting the ink from a point of said eachrecording electrode that said ink is discharged to a lower side of saideach recording electrode, and ink flow modulating room for modulating anamount of the ink flow to said each recording electrode, and a pulsevoltage generation circuit for applying the pulse voltage to said pluralrecording electrodes, and wherein said substrate, said plural recordingelectrodes, said plural control electrodes, said pulse voltagegeneration circuit, and said ink circulation part are integratedtogether.
 30. An ink jet recording head comprising: a plurality ofrecording electrodes arranged on a substrate, a plurality of controlelectrodes arranged so as to sandwich each of said recording electrodes,an ink circulation part having ink supply channel provided to flow inkwhich contains coloring material in solvent to said recording electrodesin a direction of length of said each recording electrode, inkcollection channel for collecting the ink from a point of said eachrecording electrode that said ink is discharged to a lower side of saideach recording electrode, and ink flow modulating room for modulating anamount of the ink flow to said each recording electrode, a bias supplyfor applying an electrode bias to said plural recording electrodes andsaid plural control electrodes, a pulse voltage generation circuitconnected to each of said plural recording electrodes, a recordingmedium carrying passage for carrying a recording medium, and a commonelectrode opposed to said plural recording electrodes.
 31. An ink jetrecording head comprising: a substrate, a plurality of recordingelectrodes arranged on said substrate, a plurality of control electrodesarranged so as to sandwich each of said recording electrodes, an inkcirculation part for supplying ink which contains coloring material insolvent to said recording electrodes to flow the ink in a direction of alength of respective ones of said recording electrodes and forcollecting the ink from a tip of respective ones of the recordingelectrodes, said ink circulation part including ink channels providedfor each recording electrode, the ink channels being at least partiallydelimited by shrouds.
 32. The ink jet recording head according to claim31, wherein the shrouds are shrouds of a dielectric substance.